1. Technical Field
The present invention relates to a wastewater treatment apparatus which biologically decolorizes and denitrifies wastewater containing a nitrogen-containing dye. More specifically, the invention pertains to a wastewater treatment apparatus capable of easily decolorizing and decomposing, at a low cost, a persistent nitrogen-containing dye such as an azo compound in wastewater containing a dye, being compact, having excellent durability and high processing power and ensuring long-term stable operation.
2. Description of the Prior Art
Nitrogen-containing dyes, particularly, azo dyes account for the largest proportion of all synthetic dyes. They are used in various fields such as fibers, foods and cosmetics When dye-containing wastewater discharged from dye manufacturing plants and the like is released into the environment, it colors the surrounding environment and impairs the environment and beautiful appearance. There is accordingly an increasing demand for the decolorization or detoxification of the above-described dye existing in the wastewater. Wastewater containing dyes have conventionally been treated mainly as a mixture with another wastewater by the activated sludge process under aerobic conditions. The activated sludge process however only removes BOD (Biochemical Oxygen Demand) and SS (Suspended Substance) components from the wastewater. Many dyes are persistent nitrogen-containing compounds such as azo dyes. Since they cannot be removed biologically by the activated sludge process, the wastewater has been released into the environment without removing therefrom coloring or nitrogen components derived from these dyes.
As a method of physically removing a dye-containing substance from wastewater, it is known to treat dye-containing wastewater by the activated sludge process, physically separating the dye from the wastewater by solidify the dye-containing substance with the aid of coagulating sedimentation or by adsorbing the substance onto activated charcoal or the like: and then reclaiming the dye. This method is however accompanied with such a drawback that the persistent dye which has remained undecomposed exerts a bad influence on the environment when it is released thereinto. In order to avoid such an influence, only a limited landfill site can be used.
As a method of chemically decomposing a dye-containing substance in wastewater, proposed are, for example, a method of decomposing the dye by bringing it into contact with ozone (Japanese Patent Laid-Open No. 239383/1997), a method of bringing it in contact with oxygen under humid conditions, thereby oxidizing it (Japanese Patent Laid-Open No. 253669/1997), a method of bringing it in contact with an enzyme, thereby decomposing it (Japanese Patent Laid-Open No. 2000-245468). and a method of decomposing it under supercritical conditions (Japanese Patent Laid-Open No. 2001-121137). Any one of these methods however involve drawbacks such as necessity of an extra cost for chemicals and facilities and generation of by-products which disturb treatment.
As described above, an apparatus for treating dye-containing wastewater capable of decolorizing and decomposing, at a low cost, a persistent nitrogen-containing dye such as azo compound to an extent not having an adverse environmental effect is not known. An object of the present invention is therefore to provide a wastewater treating apparatus capable of easily decolorizing and decomposing, at a low cost, a persistent nitrogen-containing dye such as azo compound in wastewater containing a nitrogen-containing dye, being compact, having excellent durability and high processing power, and ensuring long-term stable operation.